Diptera, true flies in the Mycetophilidae and Cecidomyiidae families

Mycetophilidae family, the fungus midges and fungus gnats

These are the fungus midges or fungus gnats, they were previously known as the Fungivoridae. As their name suggests they can be found in fungi and other decaying material which the larvae eat. They are found worldwide, and there are about 3400 species worldwide, and 471 British species. Adults are generally found in moist, dark places in woods, cliffs, riverbanks, caves and tunnels. Most species have a peak of activity around dusk. In colder areas many can hibernate in caves, cellars, under bark and in hollow plant stems.

In New Zealand and Australia some species have larvae that can drop a line, rather like a spider, with sticky droplets spaced down the line. These droplets trap small flying insects that the larvae then eat. Many of these larvae are luminescent.

Mycetophilidae, fungus midge, adult

All are delicate with long legs (see above) with powerful spurs, a humped thorax overhanging the head, and relatively thick, thread-like antennae. The adults are around 6 mm long with brown bodies. In some species the males dance in swarms close to the ground. Adults are common from March to August. The larvae are thin and shiny whitish with a dark coloured head, and up to 10 mm long. Some species have carnivorous larvae that eat other fungus-dwelling insects.

Cecidomyiidae family

Cecidomyiidae, adult gall midge

Above is an adult Cecidomyiidae, or gall midge or gall gnats (most are gall makers, but a few are leaf miners), they were previously known as Itonidae or Itonidsdae. These are tiny, fragile flies, rarely more than 5 mm in length. Though tiny this fly can alter the shape of a tree or plant. There are over 6000 species worldwide, and 652 British species, and over 1000 species in North America.

Cecidoyiidae larva,

Above is a rather unusual Cecidomyiidae larva, as this is a free-living species.

Most of the larva live in and cause galls on plants - hence the common name. The larva becomes completely surrounded by plant tissue - the gall - within a few days. Once the larva reaches maturity the growth of the gall ceases - so the insect controls the gall formation usually by its feeding activity. Gall midge larvae have vestigial mouthparts and absorb their nourishment by suction. The gall provides the larval insect with its food, protection from predators, and shelter from adverse environmental conditions.

In the U. K. the insect usually overwinters as a larva, and pupates in the spring.

The adults' wings are slightly hairy and sparsely veined with never more than 4 veins reaching the wing margin. The antennae are beaded, and if you look through a microscope or hand lens you will see that each bead of the antenna is separated from the next by a girdle of tiny hairs. The body colour is often orange.

Some wasps and a few beetles also cause gall formation.